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Author Topic: Honda OAP mobile, advice and guidance?  (Read 374 times)

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GastronomicKleptomaniac

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Honda OAP mobile, advice and guidance?
« on: 04 March 2021, 14:20:40 »

So I've inherited a 2004 Civic 1.6 (Executive, oh yeah). It's a lovely motor, just been stood for about 8 months or so, needs a couple of bits for MOT before I can start to use it as my work wagon (leather, fuel economy, etc - perfect). It's suspected to have a blocked cat as the exhaust is VERY hot - that's getting looked at over the weekend.

However it's also got an unusual idle issue, in that when it's stone cold it sits perfectly stable at 1000rpm or so. As soon as the temperature gauge starts to move, all hell breaks loose. It starts revving up to 2500rpm, then sits there for a few seconds, drops to 1400rpm, then fluctuates between 1400 and 2200rpm or thereabouts, for a few seconds at a time.

If I turn the air con on it will sit at whereever it was when it kicked in, at least for a minute, no fluctuating, then starts revving itself again.

I've stripped and cleaned the IACV and EGR and their connections, and the throttle body, to no avail.

I've plugged it in and there's no codes and no historic codes. So far it's done maybe 40 miles since a new battery but I'd expect the ECU to have forgotten anything earlier than that.

I've also tried putting various graphs on the Torque app on my phone but I have literally no clue what I'd be looking for there.

My things to look at so far (and also suggested by a couple of other people) - blocked cat, throwing the lambda reading out as it gets warm, making the car go mad (but no codes?); physical idle control, like the idle screw on a carb, to set the base idle; coolant temp sensor misbehaving; air leak (I've checked and can't see any obvious missing or split pipes) ; faulty EGR or IACV.

Any further thoughts before I start throwing parts at it in a main dealer fashion? :D
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Marks DTM Calib

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Re: Honda OAP mobile, advice and guidance?
« Reply #1 on: 04 March 2021, 15:15:36 »

Right so lets get some understanding behind what you have been told.

Firstly, if the cat is blocked, assuming it will even start, it will idle fine but, wont rev, no power etc.........so that's easy to prove/disprove......and hot or cold, a blocked cat is a blocked cat

Secondly, mixture lambda control is pre-cat, and the system will adjust the mixture as best it can independent of what is down stream.

So lets consider the symptoms, its ok until warmed up..........that hints that it starts to occur when the operating mode of the ECU changes. We know the systems work open loop (default fuelling with correction) until the O2 sensor starts to switch so this is a possible clue.

The cat you say is red hot, is it literally red hot or just hot (is it should be hot)

Now do check, but from memory these use a wideband O2 sensor which means they can cause all sorts of strange effects......and even make the engine run lean (which will give erratic idle and a stinking hot exhaust)............any leaks around the front pipe and manifold area?
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GastronomicKleptomaniac

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Re: Honda OAP mobile, advice and guidance?
« Reply #2 on: 04 March 2021, 15:25:30 »

Right so lets get some understanding behind what you have been told.

Firstly, if the cat is blocked, assuming it will even start, it will idle fine but, wont rev, no power etc.........so that's easy to prove/disprove......and hot or cold, a blocked cat is a blocked cat

Secondly, mixture lambda control is pre-cat, and the system will adjust the mixture as best it can independent of what is down stream.

So lets consider the symptoms, its ok until warmed up..........that hints that it starts to occur when the operating mode of the ECU changes. We know the systems work open loop (default fuelling with correction) until the O2 sensor starts to switch so this is a possible clue.

The cat you say is red hot, is it literally red hot or just hot (is it should be hot)

Now do check, but from memory these use a wideband O2 sensor which means they can cause all sorts of strange effects......and even make the engine run lean (which will give erratic idle and a stinking hot exhaust)............any leaks around the front pipe and manifold area?

It doesn't seem to be lacking power, certainly pulled up to 70mph no issues.

AIUI it's a wideband sensor (fitted from 2003 onwards, according to the interweb).

Cat isn't red hot, purely that when we were trying to find a blow on the exhaust, mate blocked the exhaust and thought it was hotter than it should have been. (That's now been fixed, back box replaced).

I'm mid "idle relearn" which may prove to be successful, but the car's been Christine so far so I'm not hopeful. Once it's running again I'll have a feel for leaks, certainly can't hear any...

Cheers Mr DTM :D
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New POD

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Re: Honda OAP mobile, advice and guidance?
« Reply #3 on: 08 March 2021, 01:15:37 »

I Once had an Astra Mk3 which would idle fine, but about 3000 Rpm would be enough to rotate th e damaged ceramic inside the cat box, so it now was cau s ing a blockage..
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omegod

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Re: Honda OAP mobile, advice and guidance?
« Reply #4 on: 08 March 2021, 07:46:12 »

I've recently solved a similar idle issue with a Honda Jazz, the Idle control vale gets stuck partially open due to gunk so the revs rise and fall, this video shows the fix and it was fairly simple to do

https://www.youtube.com/watch?v=rcyewA2-BmY
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GastronomicKleptomaniac

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Re: Honda OAP mobile, advice and guidance?
« Reply #5 on: 08 March 2021, 08:20:15 »

Update on this - as stated by omegod... Took the idle valve off again, stripped it right down and cleaned it until it was like a new penny.

Now habing had the much appreciated help of Addy, gearbox is off ready for a bearing or two to be replaced, new clutch, and it should be good to go.

Top tip though... Its easier to remove the gearbox if you split it from the engine in the right place, not stipidly by taking the wrong bolts out and trying to split the case. D'oh...
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